JP2014072952A - Linear stepping motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear stepping motor capable of ensuring the stroke of a shaft as large as possible, even in a structure where the size of the motor is cut down in the axial direction.SOLUTION: A linear stepping motor includes a rotor 150 held on the inside of stator assemblies 130, 140 in a rotatable state. The rotor 150 includes a screw nut 154 at a position offset to the front side, and the screw nut 154 is screwed over the male screw structure of a shaft 170. The rotor 150 is manufactured by injection molding a raw material of resin, with rotor magnets 152, 153 and the screw nut 154 as an insert material.

Description

  The present invention relates to a linear stepping motor.

  A linear stepping motor that moves a shaft (output shaft) in the axial direction by a stepping motor is known. As the linear stepping motor, for example, the structures described in Patent Documents 1 and 2 are known.

JP 2005-354858 A JP 10-322963 A

  In the linear stepping motor, the movement amount (stroke) in the axial direction of the shaft is an important factor. For this reason, there is also a device for setting this outside the motor without providing a mechanical stopper inside the motor. However, in this case, since there is no stop position inside the motor, there is a problem that the absolute position of the shaft cannot be defined by the motor alone, and the reproducibility of the position accuracy cannot be ensured. For example, there is a problem that the position accuracy in the shipping test data and the actual apparatus does not match.

  In addition, in order to realize a long stroke, there is a type in which a through hole in which a shaft end can protrude from the rear portion of the stator is formed. In this case, the degree of freedom of expansion of the shaft stroke increases, but the risk of occurrence of troubles such as dust entering from this hole increases. This problem can be avoided by adopting a structure in which the rear portion of the stator is closed, but in this case, a large stroke cannot be secured.

  As described above, in the stator structure in which the rear portion is sealed, the shaft stroke is inevitably limited, and the stroke is not more than the motor length at the maximum. The reason is that if the shaft moves more than the motor length, the shaft will come off from the motor. Strictly speaking, it is not possible to take a stroke longer than the distance from the position of the screw nut to the wall of the stator rear portion. The reason is that the shaft is most intruded when the shaft end end face is in contact with the stator wall, and when the shaft comes out first, the shaft end end face has reached the screw screw nut. .

  In view of such a background, an object of the present invention is to provide a linear stepping motor that can secure a shaft stroke as large as possible even when the axial dimension of the motor is truncated.

  The invention described in claim 1 is a stator unit, a rotor unit disposed in a rotatable state inside the stator unit, and an output shaft that linearly moves by converting the rotational motion of the rotor unit into linear motion. A nut portion that is provided on the inner side of the rotor unit and that is screwed with a screw portion that is formed on the output shaft, and the nut portion is on one end side or the other end side in the axial direction of the rotor unit. The linear stepping motor is characterized in that it is disposed at an offset position, and the rotor unit has an integrally molded structure made of resin using the nut portion and a magnet as an insert material. According to the first aspect of the present invention, the shaft stroke can be increased by arranging the nut in the axial direction in an offset manner.

  According to a second aspect of the present invention, in the first aspect of the present invention, the rotor unit is held in a rotatable state by a pair of bearings having the same structure on the stator unit. According to the second aspect of the invention, the parts can be shared, which is advantageous for cost reduction.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the rotor unit includes a pair of the magnets arranged at intervals in the axial direction, and the pair of the magnets between the pair of magnets. An intermediate portion having an outer diameter smaller than the outer diameter of the pair of magnets is provided. According to the third aspect of the present invention, the occurrence of an accident in which a part of the rotor comes into contact with the stator due to resin burrs or the like can be suppressed. Furthermore, the occurrence (problem) of an accident in contact with the stator due to the increase in the outer diameter of the resin due to the difference in the thermal expansion coefficient between the rotor magnet and the resin due to the temperature rise can be suppressed.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the stator unit has an integral structure molded with resin. According to the third aspect of the present invention, the manufacture of the stator unit is simplified, and the internal gap is filled with the resin, so that dust resistance is high and high reliability is obtained. In addition, the coil bobbin is integrated by the resin mold, so that vibration due to coil excitation and vibration due to motor rotation are reduced, which contributes to lower noise.

  ADVANTAGE OF THE INVENTION According to this invention, even if it is the structure which truncated the dimension in the axial direction of the motor, the linear stepping motor which can ensure the stroke of a shaft as much as possible can be obtained.

It is the top view (A) and front view (B) of embodiment. It is a sectional side view of an embodiment. It is a sectional side view of a rotor. It is a perspective view which shows the process of the assembly of embodiment.

(Construction)
1 and 2 show a linear stepping motor 100 according to an embodiment. The linear stepping motor 100 includes a front housing 101 and an end housing 102. A stator assembly 130 and a stator assembly 140 are disposed between the front housing 101 and the end housing 102. The stator assembly 130 and the stator assembly 140 have basically the same structure, and are arranged back to back in the axial direction. Stator assembly 130 and stator assembly 140 constitute a claw pole type stepping motor stator.

  Hereinafter, the stator assembly 130 will be described as a representative. The stator assembly 130 includes an outer stator 131 and an inner stator 132. The outer stator 131 and the inner stator 132 are made of a magnetic material such as an electromagnetic steel plate. The outer stator 131 and the inner stator 132 have the same structure as that in a normal claw pole type stepping motor. A stator coil 134 configured by winding a magnet wire around a resin bobbin 133 is disposed inside the outer stator 131. A terminal pin 137 is embedded in the bobbin 133. Here, the stator assembly 130 has been described, but the stator assembly 140 has a similar structure.

  The stator assemblies 130 and 140 are integrated by a resin mold structure by injecting resin into the internal gap in a temporarily assembled state. Reference numeral 136 denotes a filled resin material. With this resin mold structure, the stator assemblies 130 and 140 are integrated in a state where they are in contact with each other in the axial direction. At this time, the end-side housing 102 is also integrally formed simultaneously with the resin material 136. The end-side housing 102 is a member that closes the space inside the stator, and the movement of a shaft (described later) arranged inside the stator is restricted by the end-side housing 102.

  The front plate 135 is fixed to the stator assembly 130 in a contact state. The front plate 135 has a flange portion provided with two screw holes 135a. The linear stepping motor 100 is fixed to the fixed object using the screw hole 135a. The front side housing 101 is fixed to the front plate 135. This fixing is performed using a claw portion (locking portion) 135b provided on the front plate 135. In addition, the shape of the flange in the front plate 135 is not limited to the shape illustrated.

  As shown in the figure, the stator assembly 130 is provided with a terminal pin 137, and an end portion of a winding of the stator coil 134 is entangled and connected to the terminal pin 137. The terminal pin 137 is passed through the contact hole of the substrate 138 on which the wiring pattern is formed, and the end portion penetrates the substrate 138. The substrate 138 is integrated with the terminal portion 139, and the terminal portion 139 is fixed to the stator assemblies 130 and 140. In addition, although description is abbreviate | omitted, the terminal pin of the same structure is provided also in the stator assembly 140 side.

  Inside the stator assemblies 130 and 140, the rotor 150 is housed in a rotatable state. FIG. 3 shows a cross-sectional view of the rotor. The rotor 150 includes a rotor member 151, rotor magnets 152 and 153, and a screw nut 154. The rotor member 151 is a substantially cylindrical member formed by resin injection molding using the rotor magnets 152 and 153 and the screw nut 154 as insert materials. Bosses 156 and 157 for attaching rolling bearings 161 and 162 are provided at both ends of the rotor member 151. The resin constituting the rotor 150 may contain 10% to 50% by weight of glass filler or the like. The rotor magnets 152 and 153 are bonded magnets made of resin and magnetic powder, and have a substantially cylindrical shape. The rotor magnets 152 and 153 are alternately magnetized with the NSNS along the circumferential direction. The screw nut 154 has a female screw structure on the inner side, and this female screw structure meshes with a male screw of the shaft 170 described later.

  In FIG. 3, Lrot is a length in the axial direction of the rotor 150 (rotor length), Lmag is a length in the axial direction of the rotor magnets 152 and 153 (magnet length), and Lnut is a length in the axial direction of the screw nut 154. (Nut length). Here, Lnut <Lmag is set.

  As shown in FIG. 3, the central portion P <b> 1 of Lrot is the center position in the axial direction of the rotor 150. P1 is also the position of the center in the axial direction of the stator (stator unit) basically composed of the stator assembly 130 and the stator assembly 140. P2 is the center position of the screw nut 154 in the axial direction. Here, the offset state is obtained by shifting the positions in the axial direction without matching the positions of P1 and P2. That is, by shifting the positions of P1 and P2, a state is realized in which the position of the nut portion is offset on either the one end side or the other end side in the axial direction of the rotor unit.

  In the present embodiment, the case where two rotor magnets 152 and 153 are used as the rotor magnet has been described, but there may be one rotor magnet. In this case as well, Lnut <Lmag and an offset state in which the positions of P1 and P2 are shifted.

  Rolling bearings 161 and 162 are attached to bosses 156 and 157 provided at both ends of the rotor 150 by press-fitting. The rolling bearings 161 and 162 are the same parts, and the rotor 150 is held by the rolling bearings 161 and 162 in a freely rotatable state on the front housing 101 and the end housing 102. A metal shaft 170 is fixed inside the rotor 150. The shaft 170 functions as an output shaft movable in the axial direction. On the outer periphery of the shaft 170, a male screw structure that meshes with the female screw structure of the screw nut 170 is engraved. The shaft 170 is provided with a stopper 171 for preventing rotation. The front-side housing 101 has a space extending in the axial direction that allows the stopper 171 to move in the axial direction and restricts the stopper 171 from rotating. In this space, the stopper 171 is movable in the axial direction along its inner wall and cannot rotate with respect to the front side housing 101 (if it tries to rotate, it comes into contact with the inner wall of the front side housing 101). Yes.

(Operation)
When a driving current whose polarity is periodically reversed is applied to the stator coils of the stator assemblies 130 and 140, a driving force for rotating the rotor magnets 152 and 153 acts on the operating principle of the claw pole type stepping motor. The rotor 150 rotates. At this time, the screw nut 154 meshed with the male screw structure on the outer periphery of the shaft 170 also rotates, but the shaft 170 cannot be rotated by the function of the stopper 171, and on the other hand, the shaft 170 can move in the axial direction. According to the rotation, the shaft 170 moves in the axial direction according to the screw principle. At this time, the rotation amount of the rotor 150 is controlled by the number of pulses of the drive signal, and thereby the linear movement amount of the shaft 170 is controlled.

(Assembly process)
First, a process for obtaining the rotor 150 of FIG. 3 will be described. First, rotor magnets 152 and 153 and a screw nut 154 are disposed as inserts in a cavity of a mold (not shown). Then, the resin heated and fluidized is injected into the cavity of the mold, and injection molding is performed. The rotor 150 shown in FIG. 3 is obtained by this injection molding.

  Next, a shaft 170 shown in FIG. 4A is prepared, and the shaft 170 and the rotor 150 are coupled. The shaft 170 is provided with a male screw portion 170a, and the state shown in FIG. 4A is obtained by screwing the screw nut 154 of the rotor 150 into the male screw portion 170a.

  Next, the stator assemblies 130 and 140 are temporarily assembled, the one in that state is placed in a mold (not shown), and resin is injected into the mold. In this process, as indicated by reference numeral 136 in FIG. 2, the gap is filled with resin, and the stator assemblies 130 and 140 are integrated with the resin.

  Next, the rolling bearing 162 is fixed inside the end-side housing 102 by press-fitting (or may be fixed by an adhesive), and the front plate 135 is fixed to the stator assembly 130 by means such as plasma welding. In this way, in the state shown in FIG. 4B, a state where the member in which the shaft 170 and the rotor 150 shown in FIG. Next, the rotor 150 of the member shown in FIG. 4A is fixed to the inner ring of the rolling bearing 162 attached inside the end side housing 102. This fixing is similarly performed by press-fitting (or fixing with an adhesive). In this way, the state shown in FIG.

  As shown in FIG. 4B, the front plate 135 has four claw portions 135a. When the state shown in FIG. 4B is obtained, the front housing 101 is fixed to the front plate 135. At this time, the front housing 101 is fixed to the front plate 135 by caulking the claw portion 135b. In this way, a linear stepping motor 100 shown in FIG. 4C is obtained. Although not shown, when the state shown in FIG. 4C is obtained, the terminal portion 139 provided with the substrate 138 is attached, and the state shown in FIGS. 1 and 2 is obtained.

(Feature)
In this embodiment, when installing a screw clew nut in the rotor, use a screw nut length that is as short as possible relative to the magnet length, and place this screw nut position in front of the rotor magnet as much as possible when viewed in the axial direction. Yes. In this way, a long distance from the screw nut to the stator rear wall is ensured, and the stroke length of the shaft is increased. Further, the total length of the motor can be shortened by offsetting the screw nut to the front side. In addition, since the mold is integrally formed, by changing a part of the mold, the position of the screw nut can be freely arranged, and a linear motor that can cope with a stroke according to necessity can be provided.

The features of the linear stepping motor 100 are listed below.
(1) The same thing is used as two rolling bearings 161 and 162, and common parts are aimed at.
(2) The rotor 150 has a structure in which rotor magnets 152 and 153 and a screw nut 154 having a thread portion are integrally formed by a resin mold. According to this structure, assembly is simplified and component accuracy is improved. Further, the position of the screw nut 154 can be easily changed.
(3) Since the stator assemblies 130 and 140 are integrated with resin, the manufacturing process is simplified, and the dustproof and reliability are improved by sealing the gap with resin.
(4) The screw nut 154 is disposed at a position offset to the front side. That is, the position of the center of the screw nut 150 is on the front side from the center of the front side stator unit (stator assembly 130). According to this structure, the axial dimension of the linear stepping motor 100 main body can be shortened while ensuring the stroke of the shaft 170 (the amount of movement in the left direction in FIG. 2).
(5) A mechanism for preventing the rotation of the shaft 170 by the stopper 171; a mechanical stopper mechanism for restricting the forward movement of the shaft 170 by the front housing 101; and a mechanical stopper mechanism for restricting the movement of the shaft 170 by the retracted end by the end housing 102. Built-in.
The stopper 171 can also be regarded as a mechanical stopper mechanism that restricts forward movement by hitting the inner surface of the housing 101 and backward movement by hitting the end face of the inner ring of the rolling bearing.
(6) In the rotor 150, the outer diameter of the intermediate portion 150a between the two rotor magnets 152, 153 is smaller than the outer diameter of the magnet, and the intermediate portion 150a is lower than the outer peripheral surface of the rotor magnets 152, 153. is there. With this structure, the possibility that the rotation of the rotor 150 is hindered by resin burrs or the like constituting the rotor 150 is suppressed.
(7) The axial length Lnut of the screw nut 154 has a relationship of Lnut <Lmag with respect to the axial length Lmag of the rotor magnets 152 and 153.
(8) The external shape of the screw nut 154 is a polygon or a shape having a rotation stopper, and the screw nut 154 does not rotate idly with respect to the rotor 150.
(9) The end-side housing 102 includes a receiving portion for holding the rolling bearing 162 and has a structure formed integrally with the stator.
(10) The front housing 101 has an integral structure having a receiving portion for holding the rolling bearing 161 and a rotation stop groove for the shaft 170.
(11) The structure of the linear stepping motor 100 is particularly suitable when the outer diameter of the rotor magnets 152 and 153 is 9 mm or less.
(12) As the rotor magnets 152 and 153, sintered magnets such as ferrite magnets and rare earth magnets, and bonded magnets can be used.
(13) The thickness of the resin constituting the rotor 150 in the radial direction can be reduced as much as possible, and the motor outer diameter can be reduced. Further, the front end surface of the screw nut 154 is located behind the end surface of the rolling bearing 161.

(Other)
The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

  The present invention can be used for a linear stepping motor.

  DESCRIPTION OF SYMBOLS 100 ... Linear stepping motor, 101 ... Front side housing, 102 ... End side housing, 130 ... Stator assembly, 131 ... Outer stator, 132 ... Inner stator, 133 ... Bobbin, 134 ... Stator coil, 135 ... Front plate, 135a ... Screw Hole, 135b ... Screw hole, 136 ... Filled resin, 137 ... Terminal pin, 138 ... Substrate, 139 ... Terminal part, 140 ... Stator assembly, 150 ... Rotor, 150a ... Intermediate part between a pair of rotor magnets, 151 ... Rotor member, 152 ... rotor magnet, 153 ... rotor magnet, 154 ... screw nut, 156 ... boss, 157 ... boss, 161 ... rolling bearing, 162 ... rolling bearing, 170 ... shaft, 170a ... male screw portion, 171 ... stopper.

Claims (4)

A stator unit;
A rotor unit arranged in a rotatable state inside the stator unit;
An output shaft that linearly moves by converting the rotational motion of the rotor unit into linear motion;
A nut portion provided inside the rotor unit, and screwed with a screw portion formed on the output shaft;
The nut portion is arranged at a position offset to one end side or the other end side in the axial direction of the rotor unit,
The linear stepping motor according to claim 1, wherein the rotor unit has an integrally formed structure made of resin using the nut portion and a magnet as an insert material.   The linear stepping motor according to claim 1, wherein the rotor unit is held in a freely rotatable state by a pair of bearings having the same structure on the stator unit. The rotor unit is
A pair of the magnets arranged at intervals in the axial direction;
The linear stepping motor according to claim 1, further comprising an intermediate portion having an outer diameter smaller than an outer diameter of the pair of magnets between the pair of magnets.   4. The linear stepping motor according to claim 1, wherein the stator unit has an integral structure molded with a resin. 5.

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